In the past, various different schemes have been utilized to effect multi-speed operation of a dynamoelectric machine, such as a single phase alternating current motor or the like. For instance, some of the past multi-speed electric motors were provided with a ferromagnetic stator having two sets of different winding poles; therefore, one set of winding poles was selectively excited to effect the energization of the electric motor at one predetermined speed, and the other set of winding poles was selectively energized to effect the energization of the electric motor at another different predetermined speed. For example, in an electric motor with a stator having both a two pole and a four pole winding configuration, the synchronous speed of the electric motor when the four pole winding configuration was excited was about one-half the synchronous speed of such electric motor when its two pole winding configuration was excited.
Another past multi-speed electric motor scheme is disclosed in U.S. Pat. No. 4,030,009 issued June 14, 1977 to Halsted. In this scheme, a double-pole double-throw line switch and first and second relays were utilized to control the excitation of a low speed run winding, a high speed run winding and start windings in order to attain two speed energization of the electric motor. As the aforementioned Halsted patent is understood, the first relay placed the start winding in parallel combination with the high speed run winding until the voltage across the high speed run winding became high enough to effect the actuation of the first relay when the electric motor was initially energized by manual operation of the line switch across a power source. Upon this actuation of the first relay, the start winding was switched out of the circuit, and the electric motor thereafter ran on its high speed run windings alone. When the electric motor was operated at its low speed, the second relay placed the high speed run winding and a part of the start winding in a parallel combination with the low speed run winding. As the voltage across the low speed winding attained a predetermined value, the second relay was actuated to switch both the high speed run winding and the start winding part out of circuit with the low speed run winding, and the electric motor was thereafter energized to run on the low speed run winding alone. One of the disadvantageous or undesirable features of this past two speed motor scheme is believed to be the cost involved in utilizing two relays as well as a double-pole double-throw switch to effect the two speed energization of the motor. Further, another disadvantageous or undesirable feature of this past two speed motor scheme is believed to be that the speed sensing capabilities of the two relays inferred from the voltage across the low or high speed run windings might provide imprecise switching points for switching out the start winding.
Still another past multi-speed electric motor scheme is disclosed in U.S. Pat. No. 3,097,331 issued July 9, 1963 to J. V. Miller. As this patent is understood, one of the two speeds at which the motor may be energized was selected upon the manual operation of a single-pole single-throw line switch to place the motor across a power source. After a centrifugal switch of the motor was actuated to a pair of back contacts thereof to effect the energization of the motor at one of the two speeds thereof, the single-pole single-throw switch was again manually operated to cause a momentary interruption of the energization of the motor across the power source, and such momentary power interruption effected the actuation of a relay so as to establish the energization of the motor at the other of the two speeds thereof. One of the disadvantageous or undesirable features of this another past motor is believed to be that such motor might only be suitable for low torque applications. For instance, if the motor was first energized to its low speed, the start winding was employed to accelerate the motor from its at-rest or standstill condition to such low speed. However, when the high speed was later selected, the high speed run winding alone was available to provide the additional torque necessary to effect the acceleration of the motor from its low speed to its high speed. As is well known, some motors exhibit relatively low torque when running at a speed that is substantially different than their synchronous speed as dictated by their number of poles, and such might be the case when the high speed run winding is depended upon to effect the acceleration of a motor from its low speed to its high speed, as discussed above. Another disadvantageous or undesirable feature of the above discussed another past motor is believed to be that the start windings thereof are not utilized during the running energization of such motor so as to add torque thereto.